1. Technical Field
The present invention relates to a technology for injecting liquid from an injection nozzle.
2. Related Art
Recently, a method of incising or excising a living tissue by using liquid such as water and a physiological salt water injected from an injection nozzle toward the living tissue at a high pressure has been developed as a surgical method. A liquid injection device employed for this method includes a liquid chamber filled with liquid to be injected from the injection nozzle, and an actuator for varying the volume of the liquid chamber (JP-A-2008-082202). According to this structure, the volume of the liquid chamber decreases in accordance with operation (expansion) of the actuator. As a result, the liquid within the liquid chamber is pressurized and injected as high-pressure liquid from the injection nozzle.
However, when bubbles are contained in the liquid chamber of the liquid injection device thus constructed, these bubbles contract and absorb the pressure applied to the inside of the liquid chamber. In this case, the liquid within the liquid chamber receives only insufficient pressurization, and thus the capability of incising or excising the living tissue lowers. Therefore, when bubbles are mixed or generated in the liquid chamber, the operation needs to be temporarily stopped so as to remove the bubbles within the liquid chamber by discharge through the injection nozzle or by other methods.
Under the normal operation condition of the liquid injection device (without mixture of bubbles into the liquid chamber or other abnormal conditions), driving noise (chiefly constituted by vibration noise emitted from a component for fixing the actuator or other noise) is generated by the effect of the force produced at the time of pressurization of the liquid within the liquid chamber in accordance with the expansion of the actuator. On the other hand, when the abnormal operation condition such as mixture of bubbles into the liquid chamber occurs, the driving noise generated from the liquid injection device tends to decrease (the frequency or amplitude of the driving noise changes).
However, the tendency of the liquid injection device to decrease the driving noise in accordance with the abnormal operation condition such as mixture of bubbles is completely opposite to the general idea that large abnormal noise generates when a device is in some abnormal operation condition. Thus, an operator of the liquid injection device continues using the device without noticing occurrence of the operational abnormality (existence of bubbles within the liquid chamber) in some cases.